Field of the Invention
The present application relates generally to the field of preservation of perishable materials, such as food or tissue. Specifically, the present application is directed in some aspects to methods and apparatus for food preservation capable of preserving the freshness of food products while stored at temperatures below the products' freezing point. In other aspects the invention can be applied to storing and preserving other types of perishable materials, such as biological products, including human organs and other tissue.
Description of the Related Art
The preservation of food products is a critical aspect of public health. Among the various methods of food preservation, chilling foods helps to slow the process of decomposition and the growth of contaminating microbial species. Freezing is one of the most effective methods for ensuring the safety of food products and retaining the quality of foods over long storage periods. In spite of its effectiveness, the process of freezing and thawing poses significant problems with respect to the quality of the foods. For instance, during the freezing process ice crystallization and growth can result in irreversible damage to tissue structures in meat, fish, fruit and vegetables, such as structural ruptures and changes in osmotic pressure. Other changes observed to occur in food products during the freezing and thawing process include changes in the food's sensory properties such as color, taste, and freshness. Food products subjected to excessively prolonged freezing may also experience lipid oxidation, protein denaturation, ice recrystallization, and changes in the moisture content. These degrading effects on the quality of food products are directly related to the degree of structural damages to the food products caused by the formation, growth, and distribution of ice crystals within the food products. Such problems associated with freezing food products show the importance of controlling the formation and growth of ice crystals within food products during the storage period.
To overcome these considerable issues, freezing technologies have been developed based on the manipulation of water properties. Most of these developments are aimed at inducing the quick freezing of water by instant nucleation or at controlling the size of ice crystals through the external application of stress. To this end, several studies have examined the supercooling phenomenon under different conditions and treatments. Supercooled solutions under an electric field have also been investigated. However, none of these studies have assessed how to prolong the supercooled state in foods at freezing temperatures and during extensive storage periods.
Methods and apparatus for effectively prolonging the supercooled state in foods and other perishable materials, such as organs harvested for transplantation, would be beneficial and could enable gentler storage and transportation of perishable materials while avoiding many of the problems associated with freezing and thawing.